Feedback mechanism for an injection device

Abstract

A feedback mechanism for an injection device that is configured to deliver a medicament to a user is described. The feedback mechanism comprises a piston and a fluid chamber, and the piston is adapted to move into the fluid chamber during use of the injection device. The feedback mechanism also has a damper that is arranged to damp movement of the piston, and an indicator that is arranged to provide feedback to the user after the piston has moved a pre-determined distance into the fluid chamber.

The invention claimed is: 
     
       1. An injection device comprising:
 a medicament delivery mechanism comprising:
 a reservoir; and 
 a plunger that moves to displace medicament from the reservoir for delivery to a user during use of the injection device; and 
 
 a feedback mechanism comprising:
 a piston; 
 a fluid chamber, wherein the piston is configured to move into the fluid chamber during use of the injection device; 
 a damper configured to damp movement of the piston; and 
 an indicator configured to provide feedback to the user after the piston has moved a predetermined distance into the fluid chamber, 
 
 wherein the piston is configured to move into the fluid chamber after the plunger has moved a predetermined distance into the reservoir, and 
 wherein the injection device further comprises at least one locking arm configured to hold the piston until the plunger has reached a predetermined position, the at least one locking arm configured to release the piston after the plunger has reached the predetermined position such that the piston can move into the fluid chamber. 
 
     
     
       2. The injection device of  claim 1 , further comprising a biasing member configured to push the plunger into the reservoir during use. 
     
     
       3. The injection device of  claim 2 , wherein the biasing member is configured to act on the piston, and wherein the piston and plunger are arranged such that force applied to the piston is transferred to the plunger via the fluid chamber. 
     
     
       4. The injection device of  claim 1 , wherein the damper comprises an orifice. 
     
     
       5. The injection device of  claim 1 , further comprising a housing, and wherein the damper comprises an orifice formed in the housing. 
     
     
       6. The injection device of  claim 5 , wherein the indicator comprises a pre-stressed element configured to generate an audible sound when deflected, the pre-stressed element being mounted to the plunger and configured to be deflected as the plunger moves to displace medicament. 
     
     
       7. The injection device of  claim 1 , wherein the reservoir contains the medicament. 
     
     
       8. A method of using an injection device, the method comprising:
 delivering a medicament to a user; 
 moving a piston into a fluid chamber; 
 damping the movement of the piston; and 
 providing feedback to the user after the piston has moved a predetermined distance into the fluid chamber, 
 wherein the piston is configured to move into the fluid chamber after a plunger has moved a predetermined distance into a reservoir, and 
 wherein the injection device comprises at least one locking arm configured to hold the piston until the plunger has reached a predetermined position, the at least one locking arm configured to release the piston after the plunger has reached the predetermined position such that the piston can move into the fluid chamber.